1. Field of the Invention
The present invention relates principally to a method of manufacturing a semiconductor device in a resin molded type package process, and particularly to a chip size package technique at a wafer level.
2. Description of the Related Art
A wafer level CSP (Chip Size Package) technique has been developed in recent years, so that a wafer process (pre-process) and a package process (post-process) taken for granted that they are completely separated from each other, have been combined into one. Thus, the entire framework of LSI industries has completely changed.
The wafer level CSP has been disclosed in the April 1998 issue of the “Nikkei Microdevice”, p164-167 and the August 1998 issue of the “Nikkei Microdevice”, p44-59. This technique will be explained with reference to FIG. 8. FIG. 8 is a cross-sectional view showing a process for manufacturing a semiconductor device according to the wafer level CSP.
First of all, electrode pads are relocated in a wafer having finished a wafer process and thereafter bumps are formed. An encapsulation mold (hereinafter called “mold”) is divided into an upper mold 56 and a lower mold 58. The lower mold 58 comprises an internal mold 60 and an external mold 62. These molds are heated at 175° C. The upper mold 56 is caused to absorb a mold-release film 64. A bumps-bearing wafer 66 in which the electrode pads have been relocated, is placed over the internal mold 60 of the lower mold 58, and an encapsulating resin 68 is placed thereon (see FIG. 8(A)).
The encapsulating resin 68 is melted by heat and pressure of the mold and spread over the entire surface of the bumps-bearing wafer 66 with the electrode pads relocated therein. Further, the encapsulating resin 68 is held within the mold and cured (see FIG. 8(B)). Thereafter, the bumps-bearing wafer 66 is taken out of the mold (see FIG. 8(C)). The bumps-bearing wafer 66 formed integrally with the mold-release film 64 in this way can be obtained. When the mold-release film 64 is peeled from the bumps-bearing wafer 66, bump top portions or tops 70 are exposed (FIG. 8(D)). Thereafter, external terminals 72 are formed over their corresponding bump tops 70 (see FIG. 8(E)). The wafer is cut into each piece, so that a semiconductor device 74 is completed (see FIG. 8(F)).
Owing to the use of such a method, the wafer can be cut into each chip size after the wafer is encapsulated in one lot in the package process. Thus, the package can be reduced in size up to just the same size as each chip.
An advantageous effect is also brought about in that since the number of chips obtainable from one wafer increases when the area of each chip is reduced with advances in scale-down technology, the cost per package is reduced.
However, the above-described wafer level CSP has problems such as will be described below.
Namely, since an expensive mold was used (problem 1), it was necessary to fabricate an expensive mold again when a wafer increased in diameter. With an increase in the diameter of the wafer, a resin needed to make an improvement to high flowability so as to extend to the end of the wafer (there is a possibility that other physical properties will be degraded due to the setting of the resin to the high flowability) (problem 2). Further, the resin might remain on the bump tops according to the positions of the bumps (problem 3). The mold-release film expensive and large in environment load had to be used (problem 4). Further, since compression molding is done (problem 5), the thickness of the resin is easy to vary, and strict weight control on the encapsulating resin is required. Further, the bumps might sustain damage during molding.
With the foregoing problems in view, it is therefore an object of the present invention to provide a method of manufacturing a semiconductor device, which is capable of solving the above problems, reducing the cost of manufacturing even if a wafer increases in diameter and holding performance and reliability.
In order to achieve the above-described object, there is provided a method of manufacturing a semiconductor device, according to the present invention, which, when a wafer having a main surface on which a plurality of bumps respectively connected to a plurality of electrode pads are formed, is brought into a resin molded type package to thereby manufacture the semiconductor device, comprises:                (a) placing a sheet encapsulating material containing a thermosetting resin over the wafer so as to cover the main surface; and        (b) heating and curing the sheet encapsulating material by a heating apparatus to thereby form an encapsulating resin layer.        
Here, the placement of the sheet encapsulating material over the wafer so as to cover the main surface means that the sheet encapsulating material is placed so as to completely cover the main surface with the bumps formed thereon (this includes even a substantially complete case).
Incidentally, the heating and curing described herein includes even curing based on natural heating like the occurrence of a curing reaction due to a variation in temperature when, for example, a sheet encapsulating material held in a low-temperature state is returned to room temperature. The sunlight or the like is included as the heating apparatus.
Upon carrying out the present invention, a step for polishing the encapsulating resin layer to thereby expose the tops of the bumps may preferably be included after the step for forming the encapsulating resin layer.
Typical ones of various inventions of the present application have been shown in brief. However, the Various inventions of the present application and specific configurations of these inventions will be understood from the following description.